Potential therapies now entering clinical trials for treatment of Duchenne Muscular Dystrophy include microdystrophin gene transfer (resulting in an internally truncated dystrophin) and suppression of nonsense mutations (resulting in a full-length dystrophin). In recently completed human trials of each, we have identified significant T-cell immune responses directed at dystrophin epitopes in both treated and untreated patients. It is the overall goal of our Wellstone Muscular Dystrophy Cooperative Research Center to identify the prevalence and molecular determinants of this immunity, and to determine what role immune responses to both dystrophin and recombinant AAV may play in the success or failure of gene correction therapies. In pursuit of this goal, we propose a plan that makes use of the extensive expertise and resources of the Centers for Gene Therapy and for Vaccines and Immunity at NCH. In Project 1 (J. R.Mendell, PI), we will characterize the properties and prevalence of dystrophin-specific T-cells in DMD subjects; determine the effect of initiation of glucocorticoid therapy on modulating this response; and assess these responses in a pilot trial of vascular delivery of an AAV8.MCK.micro-dystrophin. In Project 2 (C. Walker, PI), we will assess enhancement of transgene delivery in AAV-immune individuals via transient depletion of serum neutralizing antibodies; define the role the role of CD4-I- and/or CD8+ T cells against a foreign transgene product in clearance of rAAV-transduced myocytes; and determine if transient blockade of T cell activation and expansion facilitates persistent expression of a non-self transgene. The Administrative Core (Core A; J. Mendell, PI) makes use of a cadre of staff with experience in managing collaborative trials and projects in DMD, including first-in-man trials of gene therapy. The Histopathology Core (Core C; Z. Sahenk, PI) will utilize expert staff to provide resources for the analysis of tissue from projects within this and other Weilstone Centers. The Immunology Scientific Core (Core C; C. Walker, PI) will deploy cutting-edge assays for the elucidation of T-cell function, and provide a unique resource among the Wellstone network. The Education Core (Core D; P. Martin, PI) will build upon nationally recognized graduate and post-graduate programs to provide a unique educational environment.